linux-kernel - [RFC PATCH v1 09/16] unwind_user/sframe: Enable archs with encoded SFrame CFA offsets

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Message-ID: <20250710163522.3195293-10-jremus@linux.ibm.com>
Date: Thu, 10 Jul 2025 18:35:15 +0200
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        bpf@...r.kernel.org, x86@...nel.org,
        Steven Rostedt <rostedt@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrii Nakryiko <andrii@...nel.org>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>,
        Sam James <sam@...too.org>
Subject: [RFC PATCH v1 09/16] unwind_user/sframe: Enable archs with encoded SFrame CFA offsets

Enable architectures, such as s390, which store SFrame CFA offset values
encoded, to e.g. make (better) use of unsigned 8-bit SFrame offsets.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---
 include/asm-generic/unwind_user_sframe.h | 11 +++++++++++
 kernel/unwind/sframe.c                   |  1 +
 2 files changed, 12 insertions(+)

diff --git a/include/asm-generic/unwind_user_sframe.h b/include/asm-generic/unwind_user_sframe.h
index 8cef3e0857b6..cea0410a259a 100644
--- a/include/asm-generic/unwind_user_sframe.h
+++ b/include/asm-generic/unwind_user_sframe.h
@@ -5,6 +5,16 @@
 #include <linux/unwind_user_types.h>
 #include <linux/types.h>
 
+/**
+ * generic_sframe_cfa_offset_decode - Decode SFrame CFA offset.
+ *
+ * Returns the decoded SFrame CFA offset value.
+ */
+static inline s32 generic_sframe_cfa_offset_decode(s32 offset)
+{
+	return offset;
+}
+
 /**
  * generic_sframe_set_frame_reginfo - Populate info to unwind FP/RA register
  * from SFrame offset.
@@ -48,6 +58,7 @@ static inline s32 generic_sframe_sp_val_off(void)
 	return 0;
 }
 
+#define sframe_cfa_offset_decode generic_sframe_cfa_offset_decode
 #define sframe_set_frame_reginfo generic_sframe_set_frame_reginfo
 #define sframe_sp_val_off generic_sframe_sp_val_off
 
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 43ef3a8c4c26..e8658401a286 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -220,6 +220,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 
 	UNSAFE_GET_USER_INC(cfa_off, cur, offset_size, Efault);
 	offset_count--;
+	cfa_off = sframe_cfa_offset_decode(cfa_off);
 
 	ra_off = sec->ra_off;
 	if (!ra_off && offset_count) {
-- 
2.48.1